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Editors Selection IGR 10-4

Visual function: PERG

Comment by Donald Hood on:

12015 Restoration of retinal ganglion cell function in early glaucoma after intraocular pressure reduction: a pilot study, Ventura LM; Porciatti V, Ophthalmology, 2005; 112: 20-27

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The problems involved in detecting glaucomatous damage with static automated perimetry (SAP) need not be repeated here. However, because of these problems, the search for better and more objective techniques continues. Recently, there has been renewed interest in a relatively old objective test, the pattern electroretinogram (PERG), which is recorded to a reversing black and white checkerboard or grating. Numerous human and animal studies have established a connection between the PERG and glaucomatous ganglion cell damage. In spite of this evidence, the PERG is not commonly used as an objective test for glaucoma. There are at least two reasons for this state of affairs. First, a number of studies have argued that the PERG shows too much variability in human subjects with normal vision. Second, the uninitiated find it too difficult to perform well. Renewed interest in the test has been sparked, in part, by the work of Ventura and Porciatti (145) They developed a version of the PERG technique that is relatively easy to implement in the clinic, shows good reproducibility and has been incorporated into a commercially available piece of equipment. Using their technique, Ventura et al. (146) report that 52% of a group of 200 glaucoma suspects (abnormal discs, but normal SAP) had abnormal PERGs. Further, the PERG correlated with known risk factors for glaucoma leading the authors to conclude that it may predict those patients who will develop, or show progressive, field defects. While these results are both interesting and encouraging, there are three caveats that need mentioning. First, as this study confirms, and a number of studies have reported, the PERG will be normal in a fair number, probably 25% or so, of patients with clear glaucomatous damage. We have recently argued that this false negative rate is probably inherent in all ERG measures of ganglion cell function.1 Second, the PERG is best suited for early detection, as opposed to progression, as it can be maximally affected by early damage (e.g., abstract no. 146, ref. no. 1). Third, the number of glaucoma suspects who will go on to develop glaucoma is undoubtedly lower than 52% found by Ventura et al. As they point out, a longitudinal study is needed to determine the sensitivity and sensitivity of the PERG abnormalities for identifying those suspects who will develop glaucomatous field defects. It may well be the case, as the authors suggest, that the PERG will be a useful adjunct to SAP for the early detection of glaucoma. Time and the outcome of a longitudinal study will tell.

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